Plasma-enhanced chemical vapor deposition (PECVD) processes utilize plasma energy to deposit thin films of material on a wafer. Plasma is any gas in which a significant percentage of the atoms or molecules are ionized. The plasma may be generated by different methods, for example, with a direct-current discharge, a capacitive discharge, or an inductive discharge. A capacitive discharge is a frequently used method to generate plasma and is created by RF frequency between two parallel electrodes, usually in the shape of disks. The RF may be generated at a high frequency, usually at a standard 13.56 MHz, and optionally at a low frequency, usually about 100-400 kHz.
Reactive gases, also known as precursors, are fed into the plasma. The plasma energy causes the reactive gases to decompose and form a film on the wafer surface. The use of plasma allows films to be deposited at a lower temperature than non-plasma enhanced CVD. Thus, PECVD is mainly used for the deposition of dielectric films like silicon oxide or nitride layers at low temperatures. It can be also used to deposit silicon carbide, poly-silicon or carbon layers.
PECVD processes yield good adhesion and high growth rates. By varying process parameters, film properties may be fine-tuned. Adjustable film properties include adhesion, compressive and tensile stress, hydrogen content, density, etch selectivity, step coverage, stoichiometry, and cleanliness. As interconnect size decreases, PECVD process performance and deposited film property requirements increase. Thus, improved methods and apparatus for PECVD are needed.